As Sinclair rightfully points out, the only way for a touch screen work well is to make it completely obvious which parts of the screen you're supposed to touch.

In iOS 7, Apple uses a lot of implied borders around icons, but it doesn't actually give you a button to press. Instead, it uses colors, symbols or words to distinguish touchable links, which are confusing.

Here's an example Sinclair provides where there are implied borders:

(Note: in this instance the implied borders actually work. But this isn't consistent throughout iOS 7):

Jared Sinclair"Color alone simply cannot be the way to identify a button. You don't touch a color. You touch an area," Sinclair writes. "To activate a button, you must touch a spot inside of its boundary. Text floating in the middle of vast whitespace doesn't define a boundary. Only borders define boundaries."